1. Field of the Invention
This invention relates to an intramedullary intertrochanteric fracture fixation appliance.
2. Description of the Prior Art
Appliances of this kind are well known and are shown, for example, in the Applicants' European Patent Application No. 88311746.7 (Publication No. 0 321 170) and U.S. application Ser. No. 281,730 filed Dec. 9, 198, now U.S. Pat. No. 5,176,681.
Devices of this type can comprise an intramedullary rod having an angulated opening to receive a femoral neck screw which is sometimes provided in the form of a lag screw. The intramedullary rod is fitted into the intramedullary canal of the femur and the neck screw passes through the opening in the rod, through the neck of the femur and into the head. With this kind of device, it is possible to produce tension in the neck screw to pull the head and neck of the femur together, and means can be provided to prevent the screw from rotating both during this operation and in its final position. Alternatively, some surgeons prefer to merely lock the neck screw against rotation but not against axial movement, as required for the particular patient.
One type of intramedullary intertrochanteric fracture fixation appliance of this type is known as the "Gamma Nail". This has a lag screw with a nominal 12 mm diameter shaft which produces a close sliding fit in the angulated opening in the nail. The lag thread major diameter is also nominally 12 mm. Another type, including a sleeve, is shown in U.S. Pat. No. 5,032,125.
It is usual to prepare the femoral neck (to receive the lag screw) by inserting a guide wire (typically 2-3 mm diameter) along the chosen path center line first, and then any cannulated drills or taps can be run along the guide wire. With the present Gamma Nail procedure, the implant and instrumentation manufacture and the surgical technique are all demanding of extreme precision. Furthermore, the design concept assumes the guide wire will follow a straight path.
Contrary to the manufacturers intentions, some surgeons do not leave the guide wire in until the lag screw is fully in place. In some instances they avoid using the guide wire totally. In others, when they feel the 12 mm drill begin to bind, they remove the guide wire and then continue drilling. The present invention is intended to overcome some of the difficulties referred to above.
It is known to use lag screws in existing compression hip screw devices which employ a lateral bone plate. In these constructions the lateral bone plate is provided with a shaped bore in a projecting boss within which the lag screw can slide axially but not rotate. The boss forms an integral part of the lateral bone plate and the surgeon prepares a hole in the femur to accept it. These lag screws can typically have a 12 mm major diameter on the lag thread and about 8 mm diameter on the shaft. They are produced in slightly different designs and surgical instruments, for example, drills, taps and screw drivers, exist as standard for operating them.
A further advantage of the present invention therefore is that a lag screw for use in the invention defined herein can be of such a configuration that it could also be used with a lateral bone plate. Again, with this concept the parts of the present invention can be designed so that existing lag screws of this type can be used with it. Thus, when a hospital is already using compression hip screws, they could be provided with an intramedullary nail and sleeve which could be fully compatible with their existing lag screws, thus saving hospitals from stocking new instruments and implements. It will be appreciated that this advantage is not the prime requirement of the present invention but is an additional advantage.
The present invention is intended to simplify the procedure now used to implant the type of intramedullary fracture fixation appliance.